P1214: CTPS1 ACTS AS A PROGNOSTIC BIOMARKER AND THERAPEUTIC TARGET IN MANTLE CELL LYMPHOMA
Authors: Yi-Min Ren, Jinhua Liang, Kai-Xin Du, LI Wang, Rong Wang, Jianyong LI, Wei Xu
Journal: HemaSphere (2023)

Topic: 20. Lymphoma Biology & Translational Research Background: Mantle cell lymphoma (MCL) represents 6 to 8% of non-Hodgkin’s lymphoma with generally poor prognosis. Despite some recent progress, new and effective targeted therapies are urgently needed. Cytidine triphosphate synthase 1 (CTPS1) is a critical regulatory enzyme in cytidine metabolism, catalyzing the rate-limiting step in de novo CTP synthesis. A loss-of-function mutation of CTPS1 was identified as a cause of primary immunodeficiency characterized by lymphocyte dysfunction. Targeting CTPS1 is therefore desirable in the treatment of lymphoma. However, the potential roles of CTPS1 in mantle cell lymphoma is yet to be fully explored. Aims: Herein we aim to investigate the clinical significance and the functional mechanisms of CTPS1 in MCL patients. Methods: Lymph node, bone marrow biopsy and peripheral blood specimens as well as MCL cell lines were utilized as models. Liquid chromatography-coupled tandem mass spectrometry (LC-MS/MS)-based analysis was performed to measure the steady-state level of metabolites. GSE93291 dataset and immunohistochemistry (IHC) staining was utilized to determine the relationship between expression levels of CTPS1 and patient outcome. CRISPR/Cas9 editing was employed to engineer the loss-of-function models of CTPS1 and other key enzymes involved in CTP synthesis. RNA-sequencing was employed to investigate molecular mechanism. Results: Metabolic Profiling revealed dramatically aberrant cellular abundance of metabolic intermediates in the CTP synthesis pathway. For GSE93291 analysis, a nucleotide metabolism related prognostic model was established by least absolute contraction and selection operator (LASSO) Cox regression analysis and CTPS1 was screened out by highest regression coefficient. Furthermore, IHC staining of CTPS1 in 105 MCL tissues confirmed that elevated CTPS1 expression was significantly associated with poor PFS (P=0.038) and OS (P=0.001) in MCL patients (Figure 1A and B). Multivariate Cox regression analysis showed that high CTPS1 expression was an independent prognostic indicator of both PFS (P=0.014) and OS (P<0.001).CTPS1 depletion significantly impaired outgrowth and increased apoptosis of MCL cells (Granta-519, Z-138, Jeko-1 and JVM-2), while depletion of CTPS2 which shares 75% sequence identity with CTPS1 had no effect on MCL cell proliferation, suggesting that CTPS1 is the major isozyme important for MCL survival. In primary tumor samples, we found that MYC protein levels were significantly correlated with CTPS1 protein levels (P<0.001, R=0.638). MYC knockout blocked CTPS1 mRNA and protein expression prior to induction of cell death, suggesting a requisite role of MYC for in CTPS1 transcription regulation. Remarkably, TP53 aberrant and ibrutinib-resistant MCL cells rely on cytidine metabolism. Genetic or chemical inhibition (3-deazauridine) of CTPS1 can reverse poor responsiveness of MCL cell lines to ibrutinib. Cytidine level was significantly increased in TP53-deficient MCL cells and the effect of CTPS1 inhibition on MCL cells was independent of TP53 status. Gene set enrichment analysis (GSEA) of RNA-sequencing revealed that CTPS1 inhibition induced DNA damage and apoptosis. By performing immunofluorescence and immunoblot, we found that CTPS1 inhibition can cause cGAS-STING activation, which then triggered innate immune pathway, leading to MCL cells growth inhibition.Summary/Conclusion The study identified that CTPS1-mediated cytidine metabolism plays an important role in MCL (Figure 1C). CTPS1 may serve as a prognostic biomarker and therapeutic target in MCL patients. Keywords: Mantle cell lymphoma, Lymphomagenesis